The present embodiments relate to positron emission tomography (PET).
Nuclear medicine uses radiation emission to acquire images that show the function and physiology of organs, bones or tissues of the body. Radiopharmaceuticals are introduced into the body by injection or ingestion. These radiopharmaceuticals are attracted to specific organs, bones, or tissues of interest. The radiopharmaceuticals cause gamma photons to emanate from the body, which are then captured by a detector. The interaction of the gamma photons with a scintillation crystal of the detector produces a flash of light. The light is detected by an array of optical sensors of the detector.
PET is a nuclear medicine imaging technique that uses a positron emitting radionuclide. PET is based on coincidence detection of two gamma photons produced from positron-electron annihilation. The two gamma photons travel in generally opposite directions from the annihilation site, and can be detected by two opposing detectors of a ring of detectors. Annihilation events are typically identified by a time coincidence in the detection of the two gamma photons. The opposing detectors identify a line-of-response (LOR) along which the annihilation event occurred.
PET imaging systems use discriminators to detect the timing of the annihilation events. Various types of discriminators have been used in an effort to improve the timing resolution and system sensitivity of PET imaging systems, such as time-of-flight (TOF) PET systems. In TOF PET systems, the timing resolution is sufficiently precise to measure the arrival time difference between the two gamma photons. The time difference is then used to constrain the emission point to a range along the LOR.
Unfortunately, the discriminators used in TOF PET systems often have long recovery times, during which the discriminators are unable to detect events. The dead time of a discriminator is the time during which additional events are blocked from being detected. The detector signals for events occurring during dead times create a condition referred to as “pileup,” and are typically rejected.